Butadiene-styrene copolymer tackified with oxidized isoprene polymer



Patented Jan. 18, 1949 BUTADIENE-STYRENE COPOLYMER TACKI- FIED WITHOXIDIZED ISOPRENE POLY- MZER Henry F. Palmer, Akron, Ohio, assignor toThe Firestone Tire & Rubber Company, Akron, Ohio, a. corporation of OhioNo Drawing. Application October 25, 194

Serial N0. 705,817

This invention relates to a rubber composition which is a syntheticrubber produced from butadiene and styrene which is made tacky byincorporation therein of an oxidized isoprene rubber.

The isoprene rubber may be an isoprene polymer or. a copolymer ofisoprene and styrene, such as a-copolymer produced from about 75 partsisoprene and 25 parts styrene.

The expression isoprene rubber is used here- .in torefer to rubbers madefrom isoprene and thus includes synthetic isoprene polymers while;.excluding natural rubber which, although a'polymer of isoprene, hasnever been made from isoprene.

Natural rubber, when milled and compounded} pressed together. Intheproduction of a tire, ponton, etc., from. natural rubber, the variousparts may be assembled by merely pressing one to the other, and-when soassembled will adhere during subsequent handling and vulcanization.After vulcanization there is little danger of tread or ply separation.Unfortunately, the same techniques cannot be applied to the fabricationof articles from GR-S rubber (copolymers of butadient and styrene). Thismaterial lacks tack, and great difliculty has been encountered in tryingto assemble the parts of a tire, etc., prior to vulcanization.

According to this invention tack is imparted to GR-S by incorporating in100 parts of the GR-S a relatively small amount, for example, to 25parts of an oxidized isoprene rubber. The resultant formulations arequite tacky so that rubber products, such as tires, pontons, etc., matbe assembled from components containing these formulations by merelypressing the parts together. The uncured product thus produced onsubsequent vulcanization will form a coherent whole in which there is nogreat danger of separation of the plies, etc., such as is encountered inthe tires, etc., produced from GR-S as ordinarily compounded.

The oxidized isoprene rubbers employed in the practice of this inventionmay be any of the sticky products produced by the oxidation of a rubberypolymer of isoprene or copolymer of at least about 75 parts of isopreneand up to about 25 parts of styrene (the parts being by weight). Theoxidation may be effected in various ways; for instance, by intensiveandprolonged mastication on a rubber mill in contact with air or oxygen,usually at high pressure, and preferably at 2 Claims. (01; 260-455) asomewhat elevated temperature on the order of 7 0-:200 C. Alternatively,the material may be exposed .in the form of sheets, ribbons or otherconfigurations .providing a large surface-volume ratio, to oxidizinggases at the said relatively high temperatures.

The oxidizing treatment may be carried vout to various degrees; and, ingeneral, it may bestated that a suflicient degree ofoxidation for thepurpose of this invention will have been achieved when the plasticityvalue of the isoprene rubber has been reduced to not more than 3.25 mm.(Williams Plastometer at F. for 2 minutes). The treatment may be carriedout to a still further extent, limiting consideration beingthecompletebreakdown of the rubber. to a semiliquid mass. a I ,3 The oxidizedisoprene rubber may be compounded with the GR-S according to any suit,-

able formula. The GR-S and oxidized isoprene product may be milledtogether, or if ,a solution or cement is required, theymay be dissolvedin a common solvent. Vulcanizing agents, antioxidants, etc., may beincorporated in the rubber in the usual manner. A typical compound fortire construction is produced by milling together the followingingredients.

FORMULA Parts by weight GR-S Oxidized isoprene rubber 15Mercaptobenzothiazole 1 Di-o-tolylguanidine 0.1 Softeners 10 Zinc oxide4 Sulfur 3 EPC black 15 HMF black 30 Such a compound may be cured byheating 10 minutes at 290 F. or thereabouts.

The following procedures illustrate how the isoprene rubber may beoxidized. In each instance, particular reference is made to the use ofan "oxidized isoprene polymer although the same process may be employedwith an isoprene: styrene copolymer. The oxidized isoprene rubbersobtained by the procedures described here inbelow may be used incompounding according to the above formula.

M astz'cator methods This procedureapplies to oxidation in a closedmixer. Rubber-likeisoprene polymer (or other isprene rubber) is firstplasticated (plasticized by a Gordon Plasticator) or mill-massed to aspecifled plasticity-for example, a Mooney plasticity of about 35, usingthe large rotor and plasticizing for 4 minutes at 212 F. After a restperiod of 12 hours, -pmduct is creped on a 60-inch .mill and-removed inloose rolls. batch of 350 pounds is charged to a horizontaldouble-bladed dough-type mixer equipped with a plunger and a iscontinued until the plasticity of the material" is reduced to a maximumof 13.25 mm. (Williams Plastometer at 75 F. for 2 minutes); -This' willusually require about 1% to 2 hours. The final temperature of theisoprene rubber will-beabout 2"-75-"to "300 F. The plunger is thenraised and the (mixing continued for -another if: minutes at top speedto remove excessive occluded air. I

Oven method I Alternatively; theisoprene rubber which haszbeemplasticated or massed as :abo e described is -mamilled -forexample, :325 pounds iOf rubber on mafia-inch mill rfior 2.0minutes-'and'sheeted off in 'axsheet with a thickness otno more than Ainch. I'hese sheetsare 'placed in pans and heated late-12. hours in anair oven'at 220-230 to effect oxidation. #"I he sticky oxidized isoprenerubber produced by either of the above methods 'is compounded with theGR-S according to a desired formula, such as the above, and thecompounded'rubber is then used in building up ru-bberproducts in themanner in which natural rubber has been used in the past. I I

Modifications maybe made in the specific disclosure without departingfrom the invention which is defined in the appended claims.

What I claim is: 1. The method of imparting tack to a rubbery coplymerof butadieneand styrene which comprises incorporating in} T5120 9.0parts -01 the unvulcanized copolymer about 25 to 10 parts ofunyulcanized, sticky, oxidized synthetic rubbery copolymer of '75 partsof isoprene and 25 parts of 10 styrene. I

2. 'U'ncured," tacky rubber compound which contains essentially '75 to90 parts of rubbery copolymerof butadiene and styrene and 25 to 10parts'of unyulcaznized, sticky, oxidized synthetic rubberycopo'lymer of75 parts of isoprene and 25 A parts of styrene,

1 HENRY F. PALMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name 2,035,698 Fisher Mar;21 ,:1$'362,201,273 Schoenfeld Mar. 21, i940 2,264,509 Copper Dec.'.'2, H9451OTHER REFERENCES Warden, India Rubber-World, Jam (pp.

Certificate of Correction Patent No. 2,459,761. January 18, 1949.

HENRY F. PALMER errors appear in the printed specification of the aboverrection as follows:

for the heading Masticator methods line 55, for isprene read isoprene;column 3, line 16, for th mixing; column 4, line 25, list of referencescited, for Mar. 2 1936; line 27, for Copper read 00017621,

It is hereby certified that numbered patent requiring co Column 2, line51, read Mastica'tor method; e word mixture read 1, 1936 read Mar. 31,

THOMAS F. MURPHY,

Am'atant flommiasioner of Patents.

